As illustrated in FIG. 1, a wireless communication system 1000 is known in which within a macrocell 1050 formed by a macro base station 1010, a pico base station 1020 whose transmission power is lower than the macro base station 1010 is arranged (for example, see patent documents 1 to 3).
The wireless communication system 1000 is called HetNet. HetNet is an abbreviation for Heterogeneous Network. The pico base station 1020 forms a picocell 1060 within the macrocell 1050. In this example, a terminal 1030 is connected to the macro base station 1010, and a terminal 1040 is connected to the pico base station 1020. In the following description, the terminal 1030 is also represented as a macro terminal 1030. The terminal 1040 is also represented as a pico terminal 1040.
In the HetNet, radio waves transmitted from the macro base station 1010 are interference with data signals received by the pico terminal 1040 from the pico base station 1020. Since the transmission power of the macro base station 1010 is higher than that of the pico base station 1020, the interference is easily increased.
A technology is known in which in order to reduce the interference, for example, the macro base station 1010 temporarily stops the transmission of radio waves. This technology is, for example, called eICIC (enhanced Inter-Cell Interference Coordination). In the eICIC, the wireless resource of the macrocell 1050 may not be effectively utilized.
A technology is also known in which without stopping the transmission of radio waves by the macro base station 1010, as illustrated in FIG. 2, the direction of a beam BM used for formation of the macrocell 1050 is controlled, and thus the interference is reduced. This technology is, for example, called CS/CB. CS/CB is an abbreviation for Coordinated Scheduling/Coordinated Beam forming.
The control of the direction of the beam is performed by, for example, executing precoding processing based on PM (Precoding Matrix). The precoding processing is processing in which weights for individual physical antennas are assigned to individual modulation symbols.
[Patent Literature 1] Japanese Laid-open Patent Publication No. 2013-42342
[Patent Literature 2] Japanese Laid-open Patent Publication No. 2012-138753
[Patent Literature 3] Japanese National Publication of International Patent Application No. 2012-527818